Structural joining processes used for aircraft airframe skin structure basically are either bonded or riveted. Aside from other engineering and manufacturing factors used for the selection of the appropriate joining process, bonded structure has superior aerodynamic qualities while riveted structure costs less to produce. A need for a joining process which is aerodynamically smooth and inexpensive as riveted structure has become a general goal in aircraft design. Devising a riveting process which can produce the smooth appearance of a bonded structure would satisfy both the esthetics, aerodynamics and manufacturing costs requirements. A riveting method to fulfill these needs is one which back drives the shank of the rivet on the inside surface of the aircraft structure so there are no protruding rivet heads on the exterior surface, while the head of the rivet is set in a countersunk hole so as to provide a flush and smooth exterior surface.
The standard riveting techniques used today involve one person holding the rivet with a bucking bar against the shank of the rivet while a second person with a rivet gun upsets the rivet on the exterior surface which sometimes deforms the sheet metal skin. Conventional rivet guns apply rapid impact strikes to the rivet head which sometimes overdrives the rivet causing a deformation to the skin. Single impact rivet guns can be accurately adjusted so the rivet is not over or under driven and there is no possibility of deforming the aircraft skin. Single impact rivet guns are obviously faster than the conventional rivet guns and have more precise control in upsetting the rivet.
The concept of a single impact rivet gun has been around for at least two decades, as illustrated in U.S. Pat. Nos. 4,039,034 to Wagner and 4,192,389 to Raman. In the first patent listed, the rivet gun is manually held while in the second patent the rivet gun is mounted in an overall structure which also holds the sections being riveted and the bucking bar on the opposite side of the rivet. Conventional riveting techniques involve a hand-held rivet gun with a bucking bar held on the opposite end of the rivet normally by a second person. The concept of back riveting, wherein the shank of the rivet is on the inside of the aircraft structure rather than the outside, is old as taught in U.S. Pat. No. 4,007,540 to Tyree and U.S. Pat. No. 2,312,554 to Jacques.
The concept of a single person riveting operation is generally old in the art, as taught by U.S. Pat. No. 2,559,248 to Harcourt, U.S. Pat. No. 4,967,947 to Sarh, U.S. Pat. No. 4,662,556 to Gidlund, and U.S. Pat. No. 4,759,109 to Mason et al. All of the last four mentioned patents teach a machine which holds the section of the aircraft being riveted as well as the backing bar device and the riveting gun in an automated unitary structure wherein the backing member moves with the rivet gun across the surface of the section being riveted. U.S. Pat. No. 2,312,554 to Jacques, previously mentioned, also teaches a single person riveting apparatus which again is a unitary structure like the above-mentioned four patents. In the above-mentioned patent to Sarh the bucking component and the riveting component are both mounted on a universal base wherein the bucking unit and the riveting unit are computer controlled for three axis movement in unison.
The concept of an offset rivet gun whereby the driving hammer for the rivet is offset from the axis of the piston and impact pin is taught in the above-mentioned patent to Jacques; however, it is not hand-held nor is it used to drive a rivet under an extending flange of a C-channel, as done in the present invention.